This author has recently returned from a trip to Australia, where among other things he was able to re-acquaint himself with those regions of the sky that are permanently below New Mexico’s southern horizon. Among the sights within the southern hemisphere’s nighttime sky are two cloud-like objects that look like detached sections of the Milky Way; while these haveobviously been known for millennia by the indigenous peoples in the southern hemisphere, today they are usually referred to as the Magellanic Clouds, sonamed after the Portuguese explorer Ferdinand Magellan, whose around-the-world expedition circa 1520 recorded them.

We now know that the Magellanic Clouds are separate galaxies nearby our own galaxy. The larger of the two – dubbed, for obvious reasons, the “Large Magellanic Cloud” (LMC for short) – is located some 160,000 light-years away from us, while the smaller one – the “Small Magellanic Cloud,” or SMC – is about 200,000 light-years away. Many of the features of our own galaxy, such as gas and dust clouds, star-forming regions, star clusters, hot giant stars, and so on, also appear in the Magellanic Clouds, and the study of these helps provide insights into the goings-on within our galaxy. In 1987 a supernova – an exploding giant star – appeared in the LMC, becoming in the process the closest appearance of such an object in almost four centuries, and completely revolutionizing our understanding of the supernova phenomenon.

Alan Hale(Photo: Courtesy Photo/Alan Hale)

Both Magellanic Clouds are considerably smaller than our galaxy, and they are often considered as being “companion” or “satellite” galaxies of our own. This brings to mind the questions of how long this situation has lasted, and what will happen to the Clouds in the distant future.

Recent studies, involving modern computer-modeling programs as well as data from the European Space Agency’s Gaia spacecraft (which has provided extremely precise positional measurements of well over one billion stars since its launch in 2013), havestarted to bring some clarity to these questions. Some very recently announced results suggest that the SMC, along with various other nearby “dwarf” galaxies that have been discovered within the relatively recent past, are in fact satellite galaxies of the LMC. This entire retinue of galaxies appears to be approaching our galaxy for the very first time.

This approach will continue for quite some time, until about 2 1Ž2 billion years from now when the LMC (and its companions) will collide with our galaxy and will merge with it. Such “galactic cannibalism” is how large galaxies like ours grow over time – indeed, at this very moment our galaxy is absorbing a “dwarf” galaxy in the constellation Sagittarius that wasn’t identified until just a quarter-century ago – but the merger with the LMC may well be one of the largest such events in our galaxy’s history (thus far, anyway).

A somewhat similar situation is playing out with the nearest large galaxy to ours, the Andromeda Galaxy – some 2.5 million light-years away – that is visible to the unaided eye from reasonably dark observing sites and which can be seen in our northwestern evening skies this time of year. Andromeda has many “companion” galaxies, the largest of which is located in the constellation of Triangulum (adjacent to the constellation of Andromeda); this galaxy can dimly be seen with the unaided eye from very dark rural sites.

The Triangulum and Andromeda galaxies are also approaching each other, and the recent studies indicate that this event is also happening for the first time. Unlike the situation between our galaxy and the LMC, however, Andromeda and Triangulum will apparently not come close enough to collide and merge (although there will obviously be significant gravitational effects between the two galaxies). Rather, they will likely pass by each other in about a billion years or so, although what may happen in the far distantfuture remains to be seen.

The most important element in this overall dance of the galaxies is the fact that our galaxy and Andromeda are approaching each other. It has been known for some time that our two galaxies will eventually merge and form one giant galaxy, and it has generally been believed that this event will take place about four billion years from now. However, recent analysis of the Gaia data suggests that there is a significant sideways motion of Andromeda with respect to our galaxy, and thus – at least initially – the two galaxies may slide past each other without actually colliding. But this only puts off the inevitable, as the two galaxies will indeed eventually merge, although it now appears that this will take place perhaps half a billion years later than originally thought.

As for the Triangulum galaxy, it may eventually become a “satellite” galaxy of the merger between us and Andromeda. Perhaps it may eventually itself merge with us some billions of years after that, or it may get flung away from our combined galaxy altogether. There isn’t enough information available right now that can tell us which scenario is more likely.

Due to the changes that will be taking place within our sun over the intervening billions of years, Earth will have become uninhabitable long before these events play out. But if any far-future descendants of ours are still around somewhere, they will see goings-on in whatever skies they might have that are rather different from those we see nowadays.

Alan Hale is a professional astronomer who resides in Cloudcroft. He is involved in various space-related research and educational activities throughout New Mexico and elsewhere. His web site is http://www.earthriseinstitute.org.